The simultaneous installation of multiple electrical and communication cabling in underground ducting has long posed serious problems owing to problems encountered in advancing the cabling along curves and elbows such as those commonly utilized at points of ground exit. For example, it is common practice to install three-phase electrical cabling utilizing a heavy duty tow line threaded through the ducting and attached to the 1eading end of the three cables. Desirably, the ducting is sized for the efficient housing of the three cables. However, such duct size presents serious problems at underground curves or ground exit points at the latter of which it is customary to employ a 90 degree elbow. The high tension forces acting on the hauling line and on the cables as these components bear against curved portions of the ducting develop high temperatures and severe abrasion on both the tow line, the cabling and the ducting.
Burn through of the ducting, damage to the cable insulation, or both, can occur thereby rupturing the walls of these components and permitting moisture and foreign material to enter the ducting and damaging the cable with potential serious consequences.
Efforts to resolve these problems have included the use of expensive, hot dipped galvanized steel at duct bends for these components which are typically made of larger diameter than linear duct elements. This necessitates the provision of adaptor components to interconnect the smaller linear ducting to the larger diameter bend components. Not infrequently the adaptor components cause jamming of the cabling adjacent the entrance into the smaller diameter ducting. This jamming is caused by the pronounced tendency of the multiple cables to "float" at the entrance into the smaller diameter of the bend or the adaptor. That is, the portions of the several cables at bends take positions laterally of one another with the result that their combined diameters in their side-by-side relation exceeds the internal diameter of the ducting. Serious jamming problems caused by these factors are commonly encountered with costly results.